1. Field of the Invention
This invention relates to a process for producing laminated glass from at least two glass sheets and from an interlayer thickness of a plastic film glued to the two glass sheets, according to which the plastic film is joined by calendering to a glass sheet by a hardening adhesive material and this first glass sheet provided with the plastic film is joined by calendering to the second glass sheet also by a hardening adhesive material.
2. Related Art
In the case of the process now used generally to produce panes of laminated glass, the two glass sheets are joined by calendering to a thermoplastic film, in particular polyvinyl butyral, during a prejoining process, then they are subjected to a final pressing, hot and under pressure, in an autoclave. This process occurs in a discontinuous manner and relatively expensive pressure autoclaves are necessary for this purpose. Consequently, efforts have been made time and again to achieve processes for producing laminated glass which makes it possible to abandon the autoclave process. In a process of this type, the interlayer thickness of plastic has the form of a film which must be joined to the two glass sheets with layers of hardening adhesive applied in the liquid state.
A process of the type specified above is described in the document EU-A2 0 108 632. In this known process, the adhesive material is applied on the plastic film placed on a flat support using extrusion nozzles and in the form of strips spaced from one another. The first glass sheet is then set down on the plastic film covered with strips of adhesive material and the group of layers, consisting of the flat support, the plastic film covered with adhesive and the upper glass sheet, is subjected to a first calendering operation during which the plastic film is joined, without forming bubbles, to the overlying glass sheet. The formed laminate of the upper glass sheet and of the plastic film is then lifted from its support and is turned over so that the plastic film is oriented upward. Then the adhesive material, also in the form of strips, necessary to assure the joining to the second glass sheet is applied on the plastic film. On the thickness of plastic provided with adhesive material in the form of strips is then placed the second glass sheet which, during a second calendering operation, is joined without forming bubbles to the laminate comprising the glass and the plastic. To this is added the irradiation operation intended to cause the adhesive layers to harden.
In the case of another known process for producing laminated glass using liquid adhesive materials to assure the joining of the interlayer thickness of plastic material to the glass sheets, the adhesive material is applied in excess on the interlayer thickness already glued to the first glass sheet and the second glass sheet is placed on the adhesive material and is glued to the interlayer thickness by a massive calendering pressure, the second glass sheet being temporarily unglued from the interlayer thickness on the entry side of the cylinders by the adhesive material under the influence of the calendering pressure to eliminate the occluded air (DE-AS 27 37 740).
The particular difficulty in the production of laminated glass according to said process consists, during the joining by calendering of the rigid glass sheets, in preventing in a reliable way any occlusion of air. In the case of the known process, for this reason work is performed essentially with an excess of adhesive material, the excess adhesive material forming a bead between the rigid glass sheets, immediately upstream from the nip of the cylinders and being laterally expelled from between the glass sheets at the time of calendering. However, the excess adhesive material expelled laterally and at the back end of the glass sheets during calendering clogs the installation and complicates the process.
The invention has as its object to modify the process mentioned in the introduction so as to make possible a joining of the glass sheets without bubbles economically without clogging of the installation by the adhesive material coming out at the edges.
According to the invention, this object is achieved by the fact that the adhesive material for the two adhesive layers is applied each time in the form of a coherent, uniform film of a definitive or predetermined thickness and by the fact that the first glass sheet provided with the plastic film and the second glass sheet provided with the adhesive layer are joined by calendering by means of a pair of cylinders maintaining an entry opening angle of 2.degree. to 6.degree..
The joining by calendering of the two glass sheets can essentially be performed in any position, to the extent that, using appropriate mechanical means, care is taken to maintain the necessary opening angle between the two glass sheets upstream from the nip of the cylinders. The two glass sheets are therefore introduced into the calendering nip in a flat state at this reciprocal angle, and during the calendering operation, upstream from the calendering nip, they are kept separate from one another so that said opening angle is obtained between them.
In a particularly advantageous embodiment of the invention, the process is conducted in such a way that, during the joining by calendering of the two glass sheets, the second glass sheet coated with adhesive and whose coated face is oriented upward, and the first glass sheet provided with the plastic film and whose layer of plastic is oriented downward, are introduced into the nip of the cylinders, at an orientation substantially horizontal and maintaining an entry opening angle of 2.degree. to 6.degree..
The support necessary to maintain the opening angle can, in this case, be achieved in a particularly simple way by the fact that the upper glass sheet provided with the layer of plastic is supported by rollers and/or support elements in contact with the layer of plastic, while the lower glass sheet coated with adhesive material keeps its position by the intervention of its own weight.
The process according to the invention results, in a relatively simple way, in a product entirely free of bubbles without fear of a clogging of the conveying and calendering devices by the laterally expelled adhesive material.
The invention further relates to devices suitable for the implementation of the new process.
By the expression "glass sheets" is meant essentially silicate glass sheets. If applicable, one of the glass sheets, however, can also be made of a transparent plastic, for example a polycarbonate. In addition, the process according to the invention can also be used for the production of panes of glass sheets and/or which, in addition to two silicate glass sheets, comprise another layer or covering sheet of a transparent plastic. For simplicity, there will be described below only the production of a pane of laminated glass in its simplest form comprising two silicate glass sheets and an interlayer plastic film, but the invention however is not limited to this production.